One common approach to the treatment of patients with certain kinds of cancer, such as liver cancer, is to introduce radioactive particles into the patient's circulatory system, wherein the radioactive particles are targeted to the site of the cancer. Specifically, a measured amount of radioactive isotopes are injected into the patient such that they accumulate at the site of the cancer. The lodged particles thus generate a predetermined field of radiation proximate to the location of a cancerous tumor. The particular radioactive isotope is typically selected according to the type of radiation emitted and its half-life, such that the radiation has enough range to be destructive to the adjacent tumor but does only minimal damage to more remote tissue and also such that the emission of radiation lasts for only a short, predetermined duration.
One early radioisotope was yttrium, usually in oxide form, since radioactive yttrium emits nearly 100 percent beta radiation. The yttrium oxide was initially suspended in a viscous liquid medium and introduced via injection. However, yttria's high density (5.01 gm/cm3) and its inherently irregular particle shape resulted in: a) difficulties in maintaining a homogeneous suspension (and thus treat the patient with a known and controlled radiation dosage); b) difficulties in concentrating all of the radioisotope at the tumor site (as the heavy yttrium oxide particles tend to drop out of suspension too soon and adhere to the interior of blood vessels; and c) the sharp corners and edges of yttrium oxide particles irritate surrounding tissue in localized areas, as well as interfere with the uniform distribution of the radioactive particles in the tumor to be treated.
These problems were addressed by including the treatment radioisotopes in microspheres, such as those made of resin or crystalline ceramic cores with radioactive materials coated thereonto. These microspheres tend to be relatively light (with densities lower than that of yttrium oxide particles alone). However, whenever a microsphere comprises a core material having an external surface coating which contains the radioactive isotope there is a risk that the radioactive coating may separate from the underlying microsphere core. Any mechanical breakage of the coating can release unwanted radioactivity to other parts of the human body which is highly undesirable. Further disadvantages are presented by the special handling and precautions that are necessary to coat a radioactive isotope onto a crystalline ceramic core, or to label ion exchange resin.
In still another application, microspheres have been prepared comprising a ceramic material and having a radioactive isotope incorporated into the ceramic material. While the inadvertent release of radioactive isotopes from a radioactive coating into other parts of the human body is reduced or eliminated by incorporating the radioisotopes into ceramic spheres, the latter product form is nevertheless not without its disadvantages. Processing of these ceramic microspheres is dangerous because potentially volatile radioactivity must be added to ceramic melts and the microspheres must be produced and sized while radioactive. Such processing steps increase the likelihood of accidental exposure of personnel and risk radioactive contamination of facilities.
Some of these drawbacks have been overcome by incorporating stable 89Y ion oxide form into glass microspheres and subsequently exposing them to neutron radiation to activate the 89Y to 90Y. The microspheres are then injected into the patient, where they become permanently lodged. Over time, the radioactivity of the microspheres decreases as the 90Y decays. The primary drawback of these glass microspheres is that the 90Y almost exclusively emits beta radiation which, while very desirable for tumor treatment, has a very short effective range and is thus difficult, if not impossible, to detect outside the body. Thus, it is difficult to track and accurately assess where the microspheres have ultimately lodged.
Thus, there remains a need for a radiomedical cancer treatment that is useful in the treatment of cancer or tumor bearing tissue, but which will not release a radioactive coating or isotope into remote parts of the body of the patient after administration, will not require any technicians to handle any radioactive materials during the formation and spheroidization of the microsphere, which have a density which will permit the microspheres to be suspended in a fluid suitable for injection into a human, and which may be readily traced to assure accurate delivery of the radiation treatment to the desired tumor site. The present invention addresses this need.